As it was explained, Steel Inquisitors have too many spikes resulting in a frayed Spiritweb, that is why they have a linchpin spike, removing which kills them.
Koloss have 4 iron spikes, they are a patchwork of Spiritwebs, not just stolen magical abilities but inherent physical strength of other people which results in diminished faculties apparently, which leaves them vulnerable. Removing their spikes should leave them both weaker & easier to affect them with mental Allomancy, finally killing them if all spikes are removed, I think.
Kandra only have 2 spikes, making them comparatively less open to Shardic puppetry to the others. But their base form, as Mistwraith have Cognitive blockage so again, relatively vulnerable. They'd just revert to their previous form, suffering a death of personality if they don't get back their spikes soon enough.
A spiked individual is much better off than Hemalurgic entities, only hearing Ruin's voice, which can be bad enough but really only begins to become as problematic as the other three over a long period of time or psychological vulnerability.